Analog modules
6.4 Analog input module SM 331; AI 8 x 16 Bit; (6ES7331-7NF10-0AB0)
S7-300 Automation System Module data
6-26 Manual, 08/2006, A5E00105505-04
Unused channels
For unused channels, set the "disabled" instruction at the "measuring method" parameter.
This reduces the module's cycle time.
Certain inputs of the channel group configuration may remain unused. To enable diagnostic
functions at the used channels, note the special features of those inputs outlined below:
● Measuring range 1 V to 5 V: wire the used and unused inputs of the same channel group
in parallel.
● Current measurement, 4 mA to 20 mA: wire the unused inputs of the same channel group
in series. Connect a shunt resistor to each programmed and unused channel.
● Other measuring ranges: Short-circuit the plus and minus inputs of the channel.
Wirebreak monitoring
The wire-break check is available for the voltage measuring ranges, and for the 4 mA to 20
mA current measuring range.
If you configured a measuring range of ± 5V, 1 to 5 V, ± 10 V, 4 to 20 mA , and enabled
wire-break check, the analog input module logs a wire-break event in diagnostics data when
the underflow (32768) is reached.
The module also triggers a diagnostic interrupt if you enabled diagnostics interrupts in the
program.
The lit SF LED is otherwise the only indication of the wire-break, and you must evaluate the
diagnostic bytes in the user program.
If you configured a measuring range of 4 mA to 20 mA, disabled wire-break check, and
enabled diagnostic interrupts, the module triggers a diagnostic interrupt when the underflow
value is reached.
Short-circuit to M or L
If you short-circuit an input channel to M or L, the module does not suffer any damage. The
channel continues to output valid data and does not report a diagnostics event.
Overflow, underflow and hardware interrupt limits
The limits in diagnostics reaction to overflow and underflow in certain measuring ranges
differ compared to the listed ranges starting at the chapter
Analog value representation for
analog input channels
of the manual. In certain situations the numerical methods of the
module software used to evaluate the process tags do not return values up to 32511.
Do not set any hardware interrupt limits higher than the lowest possible overflow or
underflow response limits. End of cycle interrupt starting at the chapter
Analog value
representation for analog input channels
.
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